BEIJING - China's securities regulator on Friday reiterated that it will investigate and "severely punish" major shareholders who sold shares despite a six-month ban.

Starting July 8, the government banned major shareholders, corporate executives and directors who hold more than 5 percent of a company's shares from selling stakes in listed companies for six months.

The China Securities Regulatory Commission is looking into 52 alleged cases of this ruling being flouted, spokesperson Zhang Xiaojun said at a press conference.

Zhang said the infractions have exacerbated market swings and disrupted market order, and those who ignored the rule will be punished.

The commission will also investigate allegations of insider trading and other market manipulation activity, he said.

China's stock markets continued to decline beset by shrinking turnover and greater volatility. The key Shanghai index plunged 4.3 percent on Friday following the release of weak economic data. It has declined more than 30 percent from its June peak, wiping out most of this year's gains.

As part of efforts to support the market, the government has rolled out various measures, including pouring in funds and restricting futures trading on major small-cap indices.